Method for absorbing fluids from drill cuttings

ABSTRACT

A method of treating drill cuttings at a well drilling site. The method includes separating the drill cuttings from a drilling fluid at the well drilling site; contacting the separated drill cuttings with an effective amount of an absorbent material to absorb free oil from the drill cuttings into the absorbent material; and disposing of the drill cuttings. The absorbent material may include a thermo-set phenolic resin with an open cell matrix and a heat-treated peat moss.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No. 61/684,374 filed Aug. 17, 2012, which is incorporated herein by reference in its entirety.

BACKGROUND

1. Field of the Inventive Concepts

The inventive concepts disclosed herein generally relate to a method for treating contaminated drill cuttings before disposal, and more particularly, but not by way of limitation, to a method for absorbing fluids from contaminated drill cuttings so that the drill cuttings can be safely disposed.

2. Brief Description of Related Art

In rotary drilling operations, a fluid, commonly know as drilling mud, is utilized for maintenance, cooling, and lubrication of the rotary drill bit, for maintaining a hydrostatic pressure inside the borehole to prevent blowouts, and for removing drill cuttings produced as the drill bit cuts through the formation. Drilling mud is generally a slurry of liquids and certain solids, and may be water-based or oil-based depending on the liquid used to make the slurry. Some drilling applications allow for the use of either water-based or oil-based drilling mud, while other applications require one or the other for optimal completion of the well. The type and specific composition of the drilling mud used may change during the course of the drilling operation.

Drilling mud is generally circulated through the drill pipe, through openings in the drill bit, and upward through the borehole by a drilling mud system. Drilling mud systems generally include a mud-holding tank at the well surface and a network of pumps, mixers, and mud supply lines which convey the drilling mud through the system. During rotary drilling operations, drilling mud is pumped from the mud-holding tank, through the mud supply lines, down through the well bore at the desired rate and is returned to the surface of the well bore.

The return drilling mud carries with it the drill cuttings from the bottom of the borehole. Drill cuttings comprise the solids or liquid material produced as a result of the rotary drill advancing through the well bore, and may include solids such as various size rocks fragments, soil, sand, debris, hydrocarbons, minerals, and other solids or liquids present in the formation through which the wellbore is drilled. Drill cuttings removed from a borehole may be comprised of shale, sand, hard clays, or shell and are often coated with, or contain, residual contaminants from the drilling mud, or from the borehole.

When the return drilling mud, along with the carried drill cuttings, is returned to the surface, it is delivered to a screening device known as a “shale shaker” which serves as a sieve for removing the carried drill cuttings from the drilling mud. The shale shaker, which normally sits above the mud storage area, is essentially a vibrating screen that is used to separate the drill cuttings from the return drilling mud. The drilling mud falls by gravity through the screen into the mud-holding tank, and the cuttings pass over the end of the screen. When the drill cuttings have been removed from the drilling mud by the shale shaker, the drilling mud is recirculated through the drilling mud system. The drill cuttings separated from the drilling mud are collected and conveyed into a storage tank or into a storage pit for storage, further treatment, and disposal.

A problem long encountered is that the drill cuttings which have been processed by a shale shaker retain a significant amount of fluid contaminants on their surfaces. In some instances, the cuttings are merely passed from the shale shaker into an open pit, where the solids are allowed to settle to the bottom of the pit, and the fluids rise above the solids and are skimmed off the top of the pit. However, as is often the case, when a drilling mud system such as an oil-base mud is used, the cuttings are usually coated with undesirable contaminants, e.g., oil or other hydrocarbons which adhere to the surfaces of the cuttings and are difficult to remove by settling alone. If these contaminated cuttings are disposed directly into the soil, there is a risk that fluids may leach off the cuttings and contaminate adjacent lands or groundwater. Due to this threat of possible pollution, a variety of governmental regulations have been enacted to mandate the safe disposal of drill cuttings and to regulate the use of oil-based drilling muds in drilling operations.

Several methods have been suggested to process, store, and dispose of drill cuttings. One such method involves transporting drill cuttings to off-site disposal facilities. Transporting the drill cuttings from a well site to a disposal facility, whether from an onshore or an offshore drilling location is inefficient, because of the costs and added potential for spills during transit associated with transporting the bulky, heavy drill cuttings. Further, access to some well sites, such as offshore drilling rigs, or well sites located in remote territories, is difficult, or limited. In addition, contaminated drill cuttings must still undergo some treatment to remove or render inert any associated contaminates prior to their disposal at the disposal facility. Such disposal facilities may utilize deep wells whereby hazardous waste can be injected back into the earth or mixed with chemicals, such as lye and fly ash, which render the materials acceptable for land reclamation. Disposal sites may also provide centrifuges as a means of removing fluids from the drill cuttings and rely heavily on polymers added to the effluent to render the discharge liquids safe for reintroduction into the environment.

Because of the economical and logistical challenges of transporting unprocessed drill cuttings to remote locations for processing and disposal, several attempts have been made to develop a process for decontaminating and safely disposing of drill cuttings onsite. Several systems have been developed to process drill cuttings onsite, such as by washing drill cuttings with surfactants, removing fluids by pressing, centrifuging, or compacting the drill cuttings, or by blending or mixing the drill cuttings with chemicals such as lye or ash to absorb fluids from the drill cuttings. Each of those systems, however, has disadvantages that render them unsatisfactory for wide commercial implementation.

For example, some systems are inefficient due to the non-uniform size, and highly abrasive nature of the solids present in the drill cuttings. These properties render removing fluids by mechanic means costly and inefficient, and make such mechanical devices prone to malfunctions and render them expensive to operate and maintain. Some prior art systems grind up the drill-cuttings to increase fluid-removal efficiency, but the grinding process introduces undesirable time, expense, and potential for device malfunctions. In addition, heavy equipment is difficult to transport, and increases surface area needed for the wellsite.

Other prior art systems utilize chemicals, such as surfactants, to wash the drill cuttings and remove the contaminant fluids. In some cases a portion of the surfactant solution, which is rich in fine drill cuttings and adherent drilling fluids, is run through one or more hydrocyclone separators which discharge the fine drill cuttings in solution separated from the larger, cleansed drill cuttings. However, while such techniques may be successful in cleaning the cuttings, the handling and disposal of large volumes of wash solution and the equipment necessary for washing the cuttings detract from the overall effectiveness of this type of system.

Another system suggested for offshore rigs is to burn contaminants off the cuttings with high intensity lamps. However, due to the increase risk of fire and the difficulty of exposing all surfaces of the cuttings equally to the lamps, the type of system is unfeasible in most instances.

Finally, some attempts have been made to mix or blend various materials such as clay, soil, lime, ash, or other solids with the drill cuttings, such that the fluids are retained in the resulting solid mixture and are thus prevented from leaching off the drill cuttings. The processed drill cuttings are then buried underground well above the groundwater table, but below the root depth of the local plant species. Such process is however fraught with inefficiencies. For example, large volumes and weights of expensive solid materials such as lime, lye, or ash, have to be transported to the well site. Further, the currently utilized materials are inefficient and may leach contaminants into the environment over time, resulting in potential long-term liability for oilfield operators.

Therefore, a need exists for an improved method for absorbing fluids from contaminated drill cuttings onsite. It is to such a method that the inventive concepts disclosed herein are directed.

BRIEF SUMMARY OF THE INVENTIVE CONCEPTS

The inventive concepts disclosed herein provide a method for treating contaminated drill cuttings at an onsite location by absorbing fluid contaminants from the drill cuttings, so that the dry treated cuttings can be safely disposed of onsite.

The inventive concepts disclosed herein involve separating the drill cuttings from the drilling mud and mixing the contaminated drill cuttings with an absorbent material comprising a thermo-set plastic made from a phenolic resin compound with an open cell matrix in the form of granules, prilled granules, or powders. In another version, the absorbent material may be a heat-treated peat moss. The contaminated drill cuttings will normally have some fluids, such as oil, absorbed therein, and may typically also have free fluids adhering to the various surfaces thereof. The fluids adhering to the drill cuttings will contact, and be absorbed and held by the absorbent material as the mixing takes place. After the drill cuttings and absorbent material are mixed, substantially all the free fluids are absorbed and bound by the absorbent material in the mixture. This mixture can now be safely disposed of onsite (e.g., directly into native soil), without the risk of any significant amount of fluids being washed or leaching therefrom to pollute the environment.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a schematic view of an exemplary embodiment of a system for absorbing fluids from drill cuttings according to the inventive concepts disclosed herein.

DETAILED DESCRIPTION OF INVENTIVE CONCEPTS

Before explaining at least one embodiment of the inventive concepts disclosed herein in detail, it is to be understood that the inventive concepts are not limited in their application to the details of construction and the arrangement of the components or steps or methodologies set forth in the following description or illustrated in the drawings. The inventive concepts disclosed herein are capable of other embodiments or of being practiced or carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description only and should not be regarded as limiting the inventive concepts disclosed and claimed herein in any way.

In the following detailed description of embodiments of the inventive concepts, numerous specific details are set forth in order to provide a more thorough understanding of the inventive concepts. However, it will be apparent to one of ordinary skill in the art that the inventive concepts within the disclosure may be practiced without these specific details. In other instances, well-known features have not been described in detail to avoid unnecessarily complicating the instant disclosure.

As used herein the notation “a-n” appended to a reference numeral is intended as merely convenient shorthand to reference one, or more than one, and up to infinity, of the element or feature identified by the respective reference numeral (e.g., 134 a-n). Similarly, a letter following a reference numeral is intended to reference an embodiment of the feature or element that may be similar, but not necessarily identical, to a previously described element or feature bearing the same reference numeral (e.g., 148, 148 a, 148 b, etc.). Such shorthand notations are used for purposes of clarity and convenience only, and should not be construed to limit the instant inventive concept(s) in any way, unless expressly stated to the contrary.

Further, unless expressly stated to the contrary, “or” refers to an inclusive “or” and not to an exclusive “or.” For example, a condition A or B is satisfied by anyone of the following: A is true (or present) and B is false (or not present), A is false (or not present) and B is true (or present), and both A and B is true (or present).

In addition, use of the “a” or “an” are employed to describe elements and components of the embodiments herein. This is done merely for convenience and to give a general sense of the inventive concepts. This description should be read to include one or at least one and the singular also includes the plural unless it is obvious that it is meant otherwise.

Finally, as used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

Referring now to the drawings, and more particularly to FIG. 1, a typical drilling mud system 10 is shown at a well site. During the drilling of oil and gas wells with rotary drilling rigs, drill cuttings are produced from the geologic formations encountered by a drill bit 12, mounted on a drill string 12, as drilling advances to create a borehole 16.

As borehole 16 progresses during drilling, the drilling string 12 is inserted through casing 18 down to the bottom of borehole 16. The drill string 14 forms a portion of the drilling mud line 20 used to pump drilling mud from a drilling mud storage tank 22 through the drill string 14 to the bottom of the borehole 16. The drilling mud conditions and lubricates the borehole 16 to facilitate its advancement and serves to counteract geostatic pressures in the borehole 16 encountered during drilling. Drilling mud may be made up of a number of components depending upon the properties and condition of the geologic formations encountered during drilling. Drilling mud is fluid-based and such fluid-based mud may be water-based, oil or hydrocarbon-based or synthetic-based depending upon the particular properties desired.

The casing 18 typically extends from the surface down the borehole 16 to support the borehole 16. Drilling mud discharged from the drill bit 12 is circulated to the surface via the annular space between the casing 18 and the drill string 14 and carries with it the drill cuttings produced by the drill bit 12. The drilling mud, and any carried drill cuttings, returned to the surface is transported via a mud line 24 to a shaker 26 by pumping or other transporting means. The shaker 26 is a screening device that separates the carried drill cuttings from the drilling mud. The shaker 26 may be selected from any of a number of drill cutting removal devices know in the art. Suitable drill cutting removal devices include vibratory screen shakers, also known as shale shakers, which are well known in the art. The shaker 26 may further include de-sanders, de-silters, hydrocyclones, centrifuges, and other known devices for separating the cuttings from the drilling mud. After the drilling mud flows through the shaker 26, it returns to the mud storage tank 22 via one or more mud lines 28.

The drill cuttings removed from the drilling mud by the shaker 26 may be transported via a conveyor 30 to a drill cuttings holder 32. The drill cuttings removed from the drilling mud are typically of a gravel-like consistency. Conveyors for transporting such drill cuttings are well known in the art, and as such will not be described herein in detail. However, examples of suitable conveyors that may be used to transport the drill cuttings from the shaker 26 to the drill cuttings holder 32 include gravity lines, trough and auger combinations, belt conveyors, screen conveyors, pneumatic or vacuum lines, or any other such device designed to transport aggregate materials, for example.

The drill cuttings holder 32 may be implemented as any suitable receptacle, holder, or container adapted to receive and retain drill cuttings therein. Examples of suitable structures include a lined pit, a steel tank, an unlined pit, a trailer-mounted tank, a tarp, a cement mixer, and combinations thereof, for example. One or more agitators (not shown), such as screws, augers, propellers, impellers, and combinations thereof may be implemented such that the contents of the drill cuttings holder 32 may be mixed, agitated, blended, stirred, and combinations thereof, for example. In some exemplary embodiments, the drill cuttings holder 32 may be tilted or rotated to mix the contents of the drill cuttings holder 32.

With the dill cuttings separated from the drilling mud and positioned in the drill cuttings holder 32, an absorbent material is mixed with the drill cuttings inside the drill cuttings holder 18. Adsorbent materials are materials that retain liquids on the surface of their particles by capillary action and surface tension, for example. Absorbents, in contrast, retain liquids within their molecular structure. One exemplary embodiment of the inventive concepts disclosed herein contemplates using an absorbent material comprising a thermoset foam material made from a phenolic resin compound with an open cell matrix in the form of phenolic foam granules, prilled granules, or powders, whether such absorbent material is hydrophilic or hydrophobic. It is to be understood that the inventive concepts disclosed herein are applicable to other open-celled thermoset phenolic foams, other polymeric open-celled foam materials, and combinations thereof.

Another exemplary embodiment of the inventive concepts disclosed herein contemplates using an absorbent material comprising heat-treated kiln dried peat moss and derivatives thereof. The heat-treated kiln dried peat moss may be processed such that it is hydrophobic, and may include a culture of bioremediation bacteria or other organisms, and nutrients for the bioremediation organisms, for example.

Further, in some exemplary embodiments of the inventive concepts disclosed herein, the absorbent material may comprise a thermoset foam material made from a phenolic resin compound with an open cell matrix mixed with heat-treated kiln dried peat moss and/or derivatives thereof in various proportions by weight or volume, such as 1:1; 2:1; 3:1; n:1; 1:n; 1:3; 1:2; etc., where “n” can be any number or fraction, for example. The phenolic resin compound and the heat-treated kiln dried peat moss may be mechanically mixed together, or may be chemically or physically bonded together in some exemplary embodiments of the inventive concepts disclosed herein.

Additionally, one or more additives may be used in combination with absorbent materials according to the inventive concepts disclosed herein, such as pH buffers, biocidial compounds, bacterial cultures, bioremediation starter cultures, bioremediation culture nutrients, antifreeze compounds, hydrocarbons, minerals, metals, non-metals, fibrous materials, cellulose materials, and combinations thereof, for example. It is to be understood that the absorbent material may be introduced in any form, such as bricked, powdered, granulated, or by being introduced in a container such as a sock, pillow, boom, or any other suitable container, for example. Further, in some embodiments of the inventive concepts disclosed herein, the absorbent material may be used as a liner for the drill cuttings holder 18, for example.

The absorbent material may be mixed with the drill cuttings in any suitable matter. In one exemplary embodiment, the absorbent material may be manually added to the drill cuttings holder 18 prior to the drill cuttings, simultaneously with the drill cuttings (continuously or intermittently), or after the drill cuttings are conveyed to the drill cuttings holder 18. In an exemplary embodiment, an absorbent material hopper (not shown), other suitable dispensing device (not shown), and combinations thereof, may be operatively coupled with the drill cuttings holder 18, such that absorbent material may be manually or automatically introduced into the drill cuttings holder 18, as will be understood by persons of ordinary skill in the art having the benefit of the instant disclosure. For example, the absorbent material may be introduced into the drill cuttings holder 18 in any suitable manner, such as by being blown, pumped, dumped, gravity-fed, shoveled, poured, dispensed, conveyed, and combinations thereof.

In some embodiments, the absorbent material and the drill cuttings may be introduced into the drill cuttings holder 18 in a layered manner, such as for example, by alternating layers of drill cuttings and layers of absorbent material. In other embodiments of the inventive concepts disclosed herein, the drill cuttings may be introduced in the drill cuttings holder 18 onto a base layer of absorbent material, and may or may not be blanketed with another layer of absorbent material. The amount of absorbent material used for any given amount of drill cuttings may vary depending on the particular contaminants present, the amount of remaining fluids entrained in the drill cuttings, applicable disposal regulations, and other factors, as will be understood by a person of ordinary skill in the art. It has been experimentally found that generally about 1.25 lbs of absorbent material is sufficient to absorb approximately 1 U.S. gallon of fluid, and between about 1.25 lbs and about 2.5 lbs of absorbent material is capable of absorbing substantially all fluids from approximately 1 U.S. gallon of oil-based drill cuttings. It is to be understood, however, that the above amounts may vary as the composition, surface area, and size of the drill cutting varies, and mixing methods are varied. For a particular operation, the rates at which the drill cuttings and the absorbent material, respectively, are introduced into the drill cuttings holder 18 may be determined experimentally based on a variety of factors, such as the amount of oil present in the drill cuttings, and the absorbency of the absorbent material. In one version, an excess of absorbent material is introduced into the drill cuttings holder 18 to ensure that substantially all the free oil and other fluids present on the surfaces of the drill cuttings will be absorbed.

The drill cuttings and the absorbent material may be brought into contact with each other in any suitable manner, such as by mixing, blending, stirring, or agitating to allow the absorbent material to absorb fluids from the drill cuttings. The drill cuttings and the absorbent material may be brought into contact with one another by any suitable means, mechanisms, techniques, devices, and combinations thereof, for example. In an exemplary embodiment, the drill cuttings and the absorbent material may be manually brought into contact with one another via a shovel, a rake, or any other suitable instrument. In another exemplary embodiment, a mechanical device, such as an impeller, a propeller, a screw, a shaker, an auger, a cement mixer, a conveyor belt, a rotating drum, a tumbler, a loader, a back hoe, a tractor, a bucket loader an extruder, and combinations thereof, may be used to bring the drill cuttings and the absorbent material into contact with one another for any desired length of time, and to turn and mix the drill cuttings and the absorbent material until substantially all the free fluids have been absorbed by the absorbent material.

Further, in some embodiments, pressure, heat, vibrations, surfactants, or other chemical additives may be used in combinations with any of the above methods, techniques, and devices, to maximize the surface area of the drill cuttings brought into contact with the absorbent material, for example. In other exemplary embodiments, the drill cuttings may be ground up, crushed, milled, or otherwise mechanically, thermally, or chemically processed prior to contacting the absorbent material, to increase the surface area of the drill cuttings so as to enhance the absorption of fluids by the absorbent material.

In an exemplary embodiment of the inventive concepts disclosed herein, the ratio of drill cuttings to absorbent material may be predetermined by sampling the drill cuttings and determining the appropriate amount of absorbent material needed to absorb substantially all fluids from the drill cuttings. For example, a suitable test, such as a paint filter test may be used to determine the appropriate ratio of absorbent material to drill cuttings. In another exemplary embodiment, the ratio of drill cuttings to absorbent material may be determined by gradually adding absorbent material into the drill cuttings holder 18, until no more streaks or wet drill cuttings are observed. Alternatively, periodic sampling and testing of the drill cuttings/absorbent material mixture may be utilized to determine when the optimal ratio has been reached.

The dried (de-fluidized or dehydrated) drill cuttings, along with the absorbent material, are disposed of in any suitable manner. In one exemplary embodiment, the drill cuttings and absorbent material are disposed of in-situ, such as by dumping them in a suitable landfill implemented in compliance with applicable environmental laws and regulations. In some embodiments, the drill cuttings/absorbent material mixture may be compacted, or formed into a brick, or briquette, for example. In other exemplary embodiments, the drill cuttings/absorbent material mixture may be transported to an off-site location for disposal.

Further, in some exemplary embodiments, the dried drill cuttings may be separated from the absorbent material and disposed of, and the separated absorbent material may be used as fuel source for a cement kiln, or for any other desirable fuel purpose, for example.

From the above description, it is clear that the inventive concepts disclosed herein are well adapted to carry out the objects and to attain the advantages mentioned herein as well as those inherent in the inventive concepts disclosed herein. While several embodiments of the inventive concepts disclosed herein have been described for purposes of this disclosure, it will be understood that numerous changes may be made which will readily suggest themselves to those skilled in the art and which are accomplished within the scope and spirit of the inventive concepts disclosed herein. 

What is claimed is:
 1. A method of treating drill cuttings at a well drilling site, comprising: separating the drill cuttings from a drilling fluid at the well drilling site; contacting the separated drill cuttings with an effective amount of an absorbent material comprising a thermo-set phenolic resin with an open cell matrix to absorb free oil from the drill cuttings into the absorbent material; and disposing of the drill cuttings.
 2. The method of claim 1, wherein the absorbent material is in the form of granules, prilled granules, or powders.
 3. The method of claim 1, further comprising conveying the drilling cuttings to a drill cuttings holder prior to contacting the drilling cuttings with the effective amount of the absorbent material.
 4. The method of claim 1, wherein the step of contacting the drill cuttings with the absorbent material includes the step of mixing the absorbent material with the drill cuttings.
 5. The method of claim 1, wherein the absorbent material further includes an amount of heat-treated peat moss.
 6. The method of claim 5, wherein the heat-treated peat moss is hydrophobic.
 7. The method of claim 5, wherein the heat-treated peat moss includes bioremediation bacteria.
 8. A method of treating drill cuttings at a well drilling site, comprising: separating the drill cuttings from a drilling fluid at the well drilling site; contacting the separated drill cuttings with an effective amount of an absorbent material comprising a heat-treated peat moss to absorb free oil from the drill cuttings into the absorbent material; and disposing of the drill cuttings.
 9. The method of claim 8, further comprising conveying the drilling cuttings to a drill cuttings holder prior to contacting the drilling cuttings with the effective amount of the absorbent material.
 10. The method of claim 8, wherein the step of contacting the drill cuttings with the absorbent material includes the step of mixing the absorbent material with the drill cuttings.
 11. The method of claim 8, wherein the heat-treated peat moss is hydrophobic.
 12. The method of claim 8, wherein the heat-treated peat moss includes bioremediation bacteria. 